New biogeochemical proxies in seep bivalves

Reduced compounds dissolved in seeping fluids, such as methane and hydrogen sulfide, are the main energy sources in submarine cold seep systems, where they nourish the unique chemosynthesis-based ecosystems. Chemosymbiotic bivalves are the dominant macrofauna in many of these ecosystems and have been extensively studied due to their large biomass (hundreds of individuals per square meter), their symbiotic relationships with chemotrophic bacteria (methanotrophic bivalves: methane-oxidizing bacteria; thiotrophic bivalves: sulfur-oxidizing bacteria), and because they are unique archives of biogeochemical processes. In this chapter, we briefly introduce the advancements in seep bivalve research worldwide and then summarize the trophic modes and geographic distribution of seep bivalves in the South China Sea. Thereafter, the biogeochemical processes, such as the enzymatic strategy and energy transfer of seep bivalves, are generalized by integrating the trace elements and stable isotope data of the soft tissues and their corresponding calcareous shells of seep bivalves. Overall, we highlight the past contributions and current knowledge in this field and outline opportunities and future directions to expand this area of research.Funding was provided by the National Natural Science Foundation of China (Grant: 42106059), Shanghai Sailing Program (Grant: 21YF1416800) and Chenguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission (Grant: 22CGA58).